Assign Running Count to Period in Date Table

I have a date table that I need to assign a running count on the "Fiscal_Year_And_Period" column in order to do look back calculations like last 13 periods average, last 6 periods average, last 3 period average, and current period within the same query. I know i can use a CASE expression to do the calcs if a period is within 13 periods of the current period, but I run into problems when those periods extend into the prior year. I have attached a spreadsheet showing the table I have to work with and highlighted in yellow the column I need created (want to use a CTE if possible). Please let me know if furthur clarification is needed.
Calendar.xlsx
nirajkrishnaAsked:
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als315Commented:
You can get your value as follows: year*13+period -2008*13
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nirajkrishnaAuthor Commented:
Now that is one way I never thought of solving it. Very nice!
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